Embolisms are known to result from the obliteration of a blood vessel by a blood clot or a foreign body conveyed by the blood as far as the locus where the calibre is insufficient to allow passage thereof.
In order to prevent embolisms, numerous filtering devices have already been proposed, of various configurations, adapted to be placed in the path of the blood to retain the clots or foreign bodies likely to provoke an embolism.
Such devices are disclosed in particular by Patents U.S. Pat. No. 3,952,747 or FR-A-2 573 646.
These known devices generally comprise elastic legs disposed regularly about a central axis, and of which certain are provided at one end with a hook intended to allow anchoring in the wall of the vessel.
Furthermore, the device disclosed in Patent FR-A-2 573 646 is shaped to ensure automatic centering of the filter when it is positioned; the axis of the filter substantially merging with the axis of the vein in which it is placed.
It is also known that the filter devices are generally placed in the vein temporarily or permanently, by the upper (jugular) or lower (femoral) percutaneous route, by means of various accessories (in particular, carrier and ejector). In addition, such filters are generally marketed, with their accessories, in a sterile packing.
A majority (about 90% of the cases) has employed the upper route for numerous years. At the present time, it would appear that there is a reversal of tendency.
It should be noted that, due to their non-symmetrical shapes, the filter devices used at present require different accessories depending on the route chosen for positioning them in the vein.
Now, it so happens in practice that the route initially chosen by the practitioner in charge of insertion proves to be inappropriate, which requires the use of two different sets of accessories and even the use of a second filter.
It is an object of the present invention to solve the technical problem consisting in providing a filter device of a novel design, with automatic centering, which may be placed in position temporarily or permanently, equally well by the upper or lower route with the aid of the same set of accessories, guaranteeing an efficiency at least comparable to that of heretofore known filters.